Field of the Invention
The present invention relates to a mobile communication method in a mobile communication system and, in particular, to an efficient contention-based uplink transmission method in a mobile communication system.
Description of the Related Art
Mobile communication systems have developed to provide the subscribers with voice communication services on the move. With the advance of technologies, the mobile communications have been evolved to support high speed data communication services as well as the standard voice communication services.
Recently, as one of the next generation mobile communication system, Long Term Evolution (LTE) is on the standardization by the 3rd Generation Partnership Project (3GPP). LTE is a technology designed to provide high speed packet-based communication of up to 100 Mbps and standardized almost completely now with the aim at commercial deployment around 2010 timeframe. As the LTE standard is on the verge of ratification, discussion is focused on LTE-advanced (LTE-A) with the adoption of various novel techniques to LTE. One of the newly adopted techniques is contention-based access. Since the uplink transmission is performed using the dedicated transmission resource allocated by the base station, it is typical that there is no collision. In order to allocate the dedicated uplink resource, however, the terminal has to request the base station to allocate transmission resource and this procedure causes transmission delay. In order to solve this problem, the base station is capable of allocating a part of the transmission resource as contention-based access resource. The transmission resource indicated as the contention-based access resource can be commonly used by the terminal intending to transmit data.
FIG. 1 is a diagram illustrating the architecture of an LTE or LTE-A system.
Referring to FIG. 1, the radio access network of an LTE/LTE-A system includes evolved Node Bs (eNBs) 105, 110, 115, and 120, a Mobility Management Entity (MME) 125, and a Serving-Gateway (S-GW) 130. The User Equipment (hereinafter, referred to as UE) 135 connects to an external network via eNBs 105, 110, 115, and 120 and the S-GW 130. The eNBs 105, 110, 115, and 120 correspond to legacy node Bs of Universal Mobile Communications System (UMTS). The eNBs 105, 110, 115, and 120 allow the UE to establish a radio link and are responsible for complicated functions as compared to the legacy node B. In the LTE system, all the user traffic including real time services such as Voice over Internet Protocol (VoIP) are provided through a shared channel and thus there is a need of a device which is located in the eNB to schedule data based on the state information such as UE buffer conditions, power headroom state, and channel state. Typically, one eNB controls a plurality of cells. In order to secure the data rate of up to 100 Mbps, the LTE system adopts Orthogonal Frequency Division Multiplexing (OFDM) as a radio access technology on up to 20 MHz bandwidth. Also, the LTE system adopts Adaptive Modulation and Coding (AMC) to determine the modulation scheme and channel coding rate in adaptation to the channel condition of the UE. The S-GW 130 is an entity to provide data bearers so as to establish and release data bearers under the control of the MME 125. MME 125 is responsible for various control functions and connected to a plurality of eNBs 105, 110, 115, and 120.
FIG. 2 is a diagram illustrating a protocol stack of the 3GPP LTE/LTE-A system.
Referring to FIG. 2, the protocol stack of the LTE system includes Packet Data Convergence Protocol (PDCP) 205 and 240, Radio Link Control (RLC) 210 and 235, Medium Access Control (MAC) 215 and 230, and Physical (PHY) 220 and 225. The PDCP 205 and 240 is responsible for IP header compression/decompression, and the RLC 210 and 235 is responsible for segmenting the PDCP Protocol Data Unit (PDU) into segments in appropriate size for Automatic Repeat Request (ARQ) operation. ARQ is the technique for checking whether the packet transmitted by the transmitted is received by the received successfully and retransmitting the packets received erroneously. The MAC 215 and 230 is responsible for establishing connection to a plurality of RLC entities so as to multiplex the RLC PDUs into MAC PDUs and demultiplex the MAC PDUs into RLC PDUs. The PHY 220 and 225 performs channel coding on the MAC PDU and modulates the MAC PDU into OFDM symbols to transmit over radio channel or performs demodulating and channel-decoding on the received OFDM symbols and delivers the decoded data to the higher layer. With the reference to transmission, the data input to the protocol entity is referred to as SDU (Service Data Unit), and the data output by the protocol entity is referred to as PDU (Protocol Data Unit).
FIG. 3 is a diagram illustrating a normal uplink transmission operation.
Referring to FIG. 3, if a predetermined condition such as transmission data occurrence is fulfilled, the UE 305 transmits a scheduling request to the eNB 310 to request for transmission resource allocation at step 315. When it becomes necessary to transmit the scheduling request, this is expressed that the scheduling request is triggered, and the terms ‘scheduling request’ and SR are used interchangeably. The scheduling request can be categorized into one of Dedicated Scheduling Request 9D-SR) and Random Access Scheduling Request (RA-SR). The D-SR is the scheduling request transmitted through the dedicated transmission resource allocated to the UE. The transmission resource for the D-SR is the dedicated transmission resource arriving periodically and capable of transmitting 1-bit information. The UE allocated the transmission resource for D-SR is capable of transmitting D-SR, if necessary. It may not possible to allocate the transmission resource for D-SR to all UEs, and the UE allocated no transmission resource for D-SR notifies the eNB of the presence of data to be transmitted and this is expressed that RA-SR is transmitted.
Upon receipt of the scheduling request signal, the eNB allocates uplink transmission resource to the UE. The information for use in allocation of uplink transmission resource is referred to as uplink grant, and the uplink grant is transmitted to the UE through Physical Downlink Control Channel (PDCCH) at step 320. The uplink grant is addressed to the terminal with Cell-Radio Network Temporary Identity as a UE identifier. The uplink grant includes the information on the transmission resource for the uplink transmission of the UE and MCS to be applied to the uplink transmission and the information necessary for HARQ operation such that the UE performs uplink transmission at a time point after elapse of a predetermine duration since the receipt of the uplink grant. As far as the terminal has data to be transmitted, the eNB is capable of transmitting the uplink grant to the UE continuously.
FIG. 4 is a diagram illustrating a normal contention-based access operation.
Referring to FIG. 4, the eNB 410 determines to allocate contention-based transmission resource at a certain time point at step 415. This time point may be the timing when the transmission remained without being allocated to the UE due to low traffic of the cell, as example. Since the contention-based access resource is the transmission resource allocated to unspecific UEs, the allocation is performed with a separate identifier pre-indicated (or notified to the UEs in the connected state individually) rather than C-RNTI as a unique UE ID. This identifier is referred to as CB-RNTI (Contention Based-Radio Network Temporary Identity). The eNB transmits the uplink grant addressed to the CB-RNTI at step 420. Hereinafter, the terms ‘uplink grant addressed to CB-RNTI’ and ‘contention-based uplink grant’ are used interchangeably with each other. Upon receipt of the contention-based uplink grant, if there is the data to be transmitted (425), the UE transmits the data based on the contention-based uplink grant at step 430.